The use of armor steels to provide protection against small arms is common practice within the armor industry. Armor steels are readily available, with the most widely-used materials being known as “MIL-Spec” armor steels. The most common specifications for these are: MIL-DTL-12560, Armor Plate, Steel, Wrought, Homogeneous (common name RHA); MIL-DTL-46100, Armor Plate, Steel, Wrought, High Hardness (common name High-Hard); and MIL-DTL-32332, Armor Plate, Steel, Wrought, Ultra-High-Hardness
Rather than defining the specific alloys for the steels, these specifications cite the maximum content of the primary alloying elements, along with the acceptable production tolerances for the percentages of the elements. The specifications also cite steel hardness and minimum ballistic-protection performance requirements, as well as a plethora of more mundane requirements such as steel sheet flatness, waviness, etc. The ballistic performance requirements of these specifications are rarely indicative of the desired performance against the ballistic threats for particular applications.
Many steel mills recognize a market for armor steels that provide ballistic protection exceeding the performance requirements of the MIL-Specs. In fact, the above-cited specifications are re-written as more exotic steels evolve. Examples of armor steels of high ballistic performance are those manufactured by Industeel, a subsidiary of ArcelorMittal Group, and sold under the trademark MARS (series 190, 240, 270, and 300), by SSAB Technology AB and sold under the trademark ARMOX (series 370T, 440T, 500T, 600T, and ADVANCE), and by Allegheny Technologies Incorporated and sold under the trademarks 500-MIL and 600-MIL.
Armor steels are produced in large 2.5 m×5 m (8′×16′) flat plates, heat-treated to the hardness required for the requisite ballistic performance. Armor steel plates thus produced are certified as having ballistic properties. Cutting and forming these armor steel plates into products for sale is not a trivial matter. Armor steels are extremely brittle and highly susceptible to cracking. Manufacturers of ordinary hard steel plates—plates not as hard as armor steel plates—recommend using large bend radii when forming the material, and polishing the cut edges before bending to remove any discontinuities that could become stress-concentration points.
A particularly important product made of armor steel is body armor. Body armor is typically in the form of small plates that are loaded into the pockets of vests worn by military and law enforcement personnel for protection against small arms fire.
Most body armor is either made of steel or of a ceramic and composite matrix. Steel body armor is effective against bullets fired from hand guns but, if made of armor steel, effective in stopping high powered rifle bullets, it becomes especially heavy. In addition to its weight, it is also less than comfortable because it cannot be easily formed to the contours of the body of the wearer, but is bent through small angles about a vertical axis. Ceramic and composite material, on the other hand, may be effective against both hand guns and high powered rifles and is lighter and more easily molded to have a form-fitting compound curve so it is more comfortable to wear. However, it is at least an order of magnitude more expensive than armor steel. The higher price for the better, lighter, and more effective protection unfortunately puts composite armor out of reach for all but a few of those who would benefit by having it.